Just as a note, I would probably call any of these places before just putting one in my cart and buying. Reason I say that as I've had numerous times in the past where I "found" a discontinued item on some website, put one gleefully in my cart, and... nope. So now I call, especially if it's a lesser known place.
Along these lines, I had been looking for another low-profile Fantastic Vent frame. I like that they project up above the roof less, and there is plenty of room down below (especially in the shower, which is where I had planned on putting a second one). They are hard to find. Finally I found one on a recognizable RV parts site. Yay! But just to make sure, I called. They said they'd have to call their "warehouse" (which turned out to mean they called Fantastic Vent/Dometic). But yay, they had one! So Fantastic shipped it to them, and they shipped it to me.
Hmmm, outside of the factory box clearly says "high profile base." Well, let's carefully open it... Yep, high profile (which are a dime a dozen and I could have bought with one click from Amazon much easier). Sigh. So I called them. "Are you sure?" Yes, I am, sadly. "Well, it's the lowest profile one they make." Well okay, but if the shortest building on the block is forty storeys, that doesn't make it a low building. After literally days of calling, being on hold, explaining, I FINALLY got them to issue me a call tag. They were still like "But they don't make one that's lower anymore" as if that makes it a low-profile base (and duh, that's why I called and explained they were hard to find and did they really have one as their website specified they did).
Weeks later, they refunded my purchase price but not the shipping. I decided at that point my time was more important than arguing over that part. So calling doesn't always work, but usually it does.
BTW, I finally found an "old stock" low profile frame somewhere else, which was the only part I needed. It's now sitting in my parts hoard
On the porch light though: I know some people like to keep it super original, but aside from that, I wouldn't say that light is a great design, at least IMO. I would prefer one that is a bit hooded on top, and projects more of the light down. Perhaps a potted LED fixture. From what I have read this design can be prone to leaking. I have not removed mine, but I wouldn't be surprised if there is very little faying surface, and maybe an annoyingly large hole (not sure on that though, just a hunch).
A friend has a newish Airstream and that has a really nice light over the door. It's either stainless or aluminum, hooded, and the lens faces down, so won't get a bunch of UV light and yellow or crack.
All that to say it wouldn't bother me to put on a completely different light fixture, as long as it wasn't cheesy. I realize that's a matter of taste though.